Below is a pic of my lads bike, he weighs 55 kilos.
He has been riding MX for the last year with both the lowering and widening option.
The tie rod extensions are a weak link, as one of them bent pretty badly. it did not break, but it bent to a 60 deg angle.
It would be safer to get aftermarket tie rods.
Fitting was a little difficult as the directions were poor, and 4 of the bolts supplied were too short.
It is a good idea to inspect the bolts regulary for tightness, as you should do anyway in your maintenance schedule.
The kits seem strong enough, and has been jumped over 2 metres high jumps at MX, with no signs of bending or breaking of either kit or frame.
If you are really serious about jumping, go for aftermarket A arms.
If you are short of the ready cash, the kit is a little cheaper and in my opinion will serve you well.